This invention is generally relative to a Multiple-Input-Multiple-Output (MIMO)-base multiuser Orthogonal Frequency Division Multiplexing (OFDM) multiband of Ultra Wideband (UWB) Communications for short-distance wireless broadband communications.
U.S. Federal Communications Commission (FCC) released a revision of Part 15 of Commission's rules regarding UWB transmission systems to permit marketing and operation of certain types of new products incorporating UWB technology on Apr. 22, 2002. With appropriate technologies, UWB device can operate using spectrum occupied by existing radio service without causing interference, thereby permitting scarce spectrum resources to be used more efficiently. Adapting UWB technology offers significant benefits for Government, public safety, businesses, and consumers under an unlicensed basis of operation spectrum.
In general, FCC is adapting unwanted emission limits for UWB communication devices that are significantly more stringent than those imposed on other Part 15 devices. For indoor UWB operations, FCC allows a wide variety of the UWB communication devices, such as high-speed home and business networking devices, subject to certain frequency and power limitations. An emission limitation is −10 dBm for the indoor UWB operations. The UWB communication devices must operate in the frequency band from 3.1 GHz to 10.6 GHz. In addition, the UWB communication devices should satisfy the Part 15.209 emission-mask limitations for the frequency band below 960 MHz and above 960 MHz.
For indoor UWB communication devices, Table 1 lists the FCC restrictions of the emission masks (dBm) along with the frequencies (GHz) as follows:
TABLE 1Frequency (MHz)EIRP (dBm) 0-960−41.3 960-1610−75.31610-1990−53.31990-3100−51.3 3100-10600−41.3Above 10600−51.3
FCC defines an UWB communication device device where a fractional bandwidth (FB) is greater than 0.25 given by,
                              FB          =                      2            ⁢                          (                                                                    f                    H                                    -                                      f                    L                                                                                        f                    H                                    +                                      f                    L                                                              )                                      ,                            (        1        )            where fh is the upper frequency of −10 dBm emission point, and fL is the lower frequency of −10 dBm emission point.
The center frequency Fc of an UWB transmission system is obtained by using an average of the upper and lower −10 dBm emission points as follows:
                              F          c                =                                                            f                H                            +                              f                L                                      2                    .                                    (        2        )            Furthermore, a minimum frequency bandwidth of 500 MHz must be used for any indoor UWB communication devices regardless of the center frequency.
In indoor environments, the UWB communication devices can be used for wireless broadband communications within a short-distance range, particularly for a very high-speed data transmission suitable for broadband access to networks, a device access to any devices, and Internet access to high-definite television, etc.
An UWB frequency bandwidth of 7.5 GHz from 3.1 GHz to 10.6 GHz is used as a single frequency band, an analog-to-digital (A/D) and a digital-to-analog (D/A) converter must operate at a very-high sampling rate F, so that an UWB communication transceiver can be directly implemented in a digital domain. However, this leads to a very-high requirement for the A/D and D/A converter in an UWB transmitter and receiver. Presently, developing such a very high-speed A/D and D/A converter may not be possible with a reasonable cost, thereby having a difficult problem to apply the A/D and the D/A converter for the UWB communication transceiver based on the single frequency band. On the other hand, a single frequency band-based UWB communication transceiver may not have flexibility and scalability for transmitting and receiving a user data. In addition, the single frequency band-based UWB communication transceiver may have interference with a Wireless Local Area Network (WLAN) 802.11a transceiver without using a special filter system since the WLAN 802.11a transceiver operates at a lower U-NII frequency range from 5.15 GHz to 5.35 GHz and at an upper U-NII upper frequency range from 5.725 GHz to 5.825 GHz.
Furthermore, since FCC is adapting unwanted emission limits for indoor UWB communication devices that are significantly more stringent than those imposed on other Part 15 devices, transmitting distance of the indoor UWB communication devices is limited if employing a convention approach, such as a single antenna for the single frequency band in the UWB communication devices. As a result, transmitting distance is approximately in a range of one meter to ten meters depending on a transmitting data rate.
An OFDM is an orthogonal multicarrier modulation technique that has been extensively used in a digital audio and video broadcasting, and a WLAN 802.11a. The OFDM has its capability of multifold increasing symbol duration. With increasing the number of subcarriers, the frequency selectivity of a channel may be reduced so that each subcarrier experiences flat fading. Thus an OFDM approach has shown in a particular useful for wireless broadband communications over fading channels.
A direct sequence spread spectrum (DSSS) is to use a pseudorandom (PN) sequence to spread a user signal. The PN sequence is an ordered stream of binary ones and zeros that referred to as chips rather than bits. The DSSS can be used to separate signals coming from multiuser. Thus the multiple access interference (MAI) among multiuser can be avoided if a set of PN sequences is designed with as low crosscorrelation as possible.
A MIMO is a multiple-input-multiple-output as a wireless link and is also a space-time signal processing so that a natural dimensional of transmitting data is complemented with a spatial dimension inherent in the use of multiple spatially distributed antennas. Thus, the MIMO is able to turn multipath propagation into a benefit for a user. In a MIMO communication system, signals on transmitter antennas at one-end and receiver antennas at the other-end are integrated in such a way that the quality of bit error rate (BER), data rate of communication for each user, or transmitting distance is improved, thereby enhancing a communication network's quality of service.
A MIMO-based multiuser OFDM multiband for an UWB communication transceiver system is disclosed herein according to some embodiments of the present invention. The present invention uses eleven frequency bands as a multiband, each of the frequency bands having 650 MHz frequency bandwidths. Each of the frequency bands employs an OFDM modulation for a multiuser UWB communication transceiver. A base station of UWB communications employs eleven antennas while a mobile station of the UWB communications uses two antennas. A solution of MIMO-based OFDM multiband allows using a set of low-speed A/D and D/A converters in parallel. A unique of the PN sequences is assigned to each user so that multiuser can share the same frequency band or the multiband to transmit and receive information data. An orthogonal sequence is also used to spread the data within each of the frequency bands, thereby leading to multiband orthogonality. On the other hand, since the OFDM is an orthogonal multicarrier modulation, subcarriers within each of the frequency bands may be flexibility turned on or off avoiding the interference with the WLAN 802.11a during the indoor UWB operations. In addition, the MIMO-based multiuser OFDM multiband of the UWB communication transceiver system improves the capability of transmitting very-high data rate in a much longer distance than the convention approach does. Moreover, the present invention of the MIMO-based multiuser OFDM multiband of the UWB communication transceiver system has a scalability to transmit and receive the data rate of 2.770 Gbps by using one of the frequency bands up to the data rate of 11.082 Gbps by using all of the eleven frequency bands.
Thus, there is a continuing need of the MIMO-based multiuser OFDM multiband of the UWB communication transceiver system for transmitting a very-high data rate in a greater distance range in indoor environments.